Cutting Edge: Recognition of Gram-Positive Bacterial Cell Wall Components by the Innate Immune System Occurs Via Toll-Like Receptor 2

TLDR

Gram‑positive and Gram‑negative bacterial infections frequently cause septic shock, yet the initial innate immune mechanisms for Gram‑positive bacteria remain poorly defined, whereas Gram‑negative LPS is known to activate CD14 and TLR2/4. The study aimed to test whether Gram‑positive bacteria are recognized by Toll‑like receptors. The authors examined whether soluble peptidoglycan from *S. aureus* activates Toll proteins.

Abstract

Abstract Invasive infection with Gram-positive and Gram-negative bacteria often results in septic shock and death. The basis for the earliest steps in innate immune response to Gram-positive bacterial infection is poorly understood. The LPS component of the Gram-negative bacterial cell wall appears to activate cells via CD14 and Toll-like receptor (TLR) 2 and TLR4. We hypothesized that Gram-positive bacteria might also be recognized by TLRs. Heterologous expression of human TLR2, but not TLR4, in fibroblasts conferred responsiveness to Staphylococcus aureus and Streptococcus pneumoniae as evidenced by inducible translocation of NF-κB. CD14 coexpression synergistically enhanced TLR2-mediated activation. To determine which components of Gram-positive cell walls activate Toll proteins, we tested a soluble preparation of peptidoglycan prepared from S. aureus. Soluble peptidoglycan substituted for whole organisms. These data suggest that the similarity of clinical response to invasive infection by Gram-positive and Gram-negative bacteria is due to bacterial recognition via similar TLRs.